Polyphenylene ether resins comprise a class of thermoplastics which are characterized by outstanding physical properties, including hydrolytic stability, excellent dielectic properties, broad temperature use range and dimensional stability at elevated temperatures. They can be made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. In general, they are prepared by the oxidative coupling of a phenolic compound with a complex copper catalyst. By way of illustration, descriptions of the preparation of polyphenylene ether resins are contained in Hay, U.S. Pat. No. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. No. 3,257,357 and 3,257,358, which are incorporated herein by reference.
In the Hay patents, the polyphenylene ether resins are prepared by oxidative coupling comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. In the Stamtoff patents, the polyphenylene ethers are prepared by reacting the corresponding phenolate ion with an initiator, e.g., an acid peroxide, in the presence of a complexing agent.
Disclosures relating to the preparation of polyphenylene ether resins using metal catalysts which do not include amines are found in Wieden et al, U.S. Pat. No 3,442,885 (copperamidines), Nakashio et al, U.S. Pat. No. 3,573,257 (metal-alcoholates or metal phenolates), and Kobayashi et al, U.S. Pat. No. 3,455,880 (cobalt chelates). The preparation of polyphenylene ethers by a non-catalytic process, e.g., oxidation with lead dioxide, silver oxide, and the like, is described in Price et al, U.S. Pat. No. 3,382,212. The disclosures of all of these references are incorporated herein by reference, to save unnecessary detail.
The processing of polyphenylene ether resins on injection molding and extrusion equipment is enhanced when the polyphenylene ethers are combined with styrene resins, e.g., crystal homopolystyrene or rubber-modified high-impact polystyrenes. These polymers are combinable in a wide range of proportions, e.g., from 1 to 99 parts of polyphenylene ether and from 99 to 1 parts of styrene resin. Compositions comprising from 10 to 60 parts of polyphenylene ether and 90 to 40 parts of styrene resin offer an especially wide range of desirable design properties. Such combinations are disclosed in Cizek, U.S. Pat. No. 3,383,435, which is incorporated herein by reference. The thermoplastic compositions disclosed in Cizek can include a rubber-modified high-impact styrene resin, as well as a homopolystyrene. High-impact styrene resins are especially useful in providing polyphenylene ether compositions which possess good resistance to impact.
It has now been surprisingly discovered that when compositions of a polyphenylene ether resin and a styrene resin are blended with a radial teleblock copolymer of a vinyl aromatic compound and a conjugated diene, e.g., a styrene-butadiene radial teleblock copolymer, the resulting compositions provide molded articles of greater impact strength. The radial teleblock copolymers of the present invention have been found to be compatible with, and effective for, compositions of relatively high polyphenylene ether resin content, e.g., 50 parts by weight or more, and low molecular weight crystal polystyrene, as well as compositions of relatively low polyphenylene ether resin content, e.g., 35 parts by weight or less, and high-impact polystyrene.
As used herein, the term "radial teleblock copolymer" refers to branched polymers having segments, or blocks, which are comprised of a conjugated diene polymer, blocks of a vinyl aromatic polymer, and a coupling agent. More particularly, in the copolymer structure, several chains of the diene polymer, usually three or more, extend from a coupling agent, with each chain terminating at its other end with a block of the vinyl aromatic polymer. It is generally believed that incompatibility of the block segments in the radial teleblock copolymer promotes the formation of a two-phase system with blocks of the vinyl aromatic polymer coalescing to form discrete regions, or "domains". These domains simulate the effect of cross-links between the chains of elastomer, and a branched elastomeric network is thus formed comprising blocks of a conjugated diene polymer, blocks of vinyl aromatic polymer, and a coupling agent.
Radial teleblock copolymers are known in the art. For instance, detailed descriptions of these materials are given by Marrs et al in ADHESIVES AGE, December, 1971 pp. 15-20 and by Haws et al in RUBBER WORLD, January, 1973, pp. 27-32, the disclosures of which are incorporated by reference.